1. Field of the Invention
The present invention relates to an internal combustion engine equipped with a sub-suction path to produce a swirl of suction gas in the combustion chamber, more specifically to a 4-cycle internal combustion engine in which the number of inlets to the sub-suction path and their opening positions are selected such that in the medium-load driving range where EGR (exhaust gas recirculation) is particularly active, a stable combustion is assured with an untimely supply of fuel being prevented; and fuel consumption can be reduced.
2. Description of the Prior Art
The latest requirements with auto internal combustion engines are exhaust gas purification, substantial reduction of NO.sub.x in particular and better fuel economy. For this purpose, EGR and lean combustion are often adopted. In this connection it has been well-known that the burning speed has only to be raised to avoid fluctuations in burning or misfiring while meeting the requirements of both much EGR and lean combustion.
Several proposals have been made to provide a sub-suction path separately from the main suction path so that the sub-suction path may serve to suck the gas and inject it into the combustion chamber, thereby producing a swirl of the suction gas in the combustion chamber, for the purpose of raising the burning speed.
The suction system having the proposed sub-suction path, however, is still in the stage of being developed to practical application and leaves much to be studied hereafter. As a matter of fact, the location of the inlet to such a sub-suction path in the conventional internal combustion engine has been inproper and caused various inconveniences depending on the mode of operation. In the conventional engine there is only one inlet to the sub-suction path and this inlet is located either closer to the atmosphere side than the carburetor venturi or within the carburetor duct between the carburetor venturi and the throttle valve. In the former location, the volume of the air passing through the carburetor venturi where the main fuel nozzle opens is naturally less and in consequence an untimely or delayed supply of fuel from the main fuel nozzle takes place especially in the medium or high load operation, and the engine response to the accel pedal action becomes poor. Further, if the opening area of the inlet is designed to match the necessary volume of gas to be injected from the sub-suction path for the medium load operation with much EGR, in time of idling a relatively large amount of the air will be supplied from the sub-suction path in spite of the small amount of the fuel supplied from the carburetor, which will result in an extremely high A/F ratio and accordingly a high possibility of misfiring.
In the latter location, the whole air flowing into the sub-suction path will be introduced through the carburetor venturi, but on account of the throttling effect of the venturi, the necessary volume of suction gas coming from the sub-suction path for the medium load operation will diminish, failing to cause a sufficient swirl. Meanwhile, in time of idling, the air passing through the venturi will suck up the fuel out of the main fuel nozzle and in consequence an excessive fuel in addition to the mixed gas from the idle port will come from the main fuel nozzle, which is unfavourable for fuel economy.